1. Field of the Invention
The present invention relates to an apparatus for stacking and storing sheets and particularly to an apparatus for stacking and storing a large amount of sheets ejected from a copying machine, a printer or the like.
2. Description of Related Art
In general, an image forming system such as an electrophotographic copying machine and a laser printer is provided with an apparatus for stacking and storing sheets on which images have been formed, either directly or after performing a stapling process on the sheets. In recent years, the capacity of such an apparatus has become larger. In a sheet storing apparatus having a large capacity, a sheet stacking tray can be elevated and lowered, whereas ejecting rollers for ejecting a sheet onto the tray are fixed at an established height. In order to stack on the tray neatly, there is provided a sensor for detecting the uppermost surface of the stack of sheets on the tray, and the tray is lowered so that the uppermost surface of the stack of sheets is detected at a constant height by the sensor.
Lowering a tray loaded with a large a mount of sheets, which have a considerable weight, requires a high-output motor, a sturdy power train and a sturdy support structure, thus increasing the size and cost of the apparatus.